I. Field of the Invention
This disclosure relates generally to systems, apparatus and methods for wireless determination of an altitude of a mobile station, and more particularly to determine an altitude of a mobile station based on a barometric pressure sensor measurement at one or more base stations and at the mobile station.
II. Background
Barometric pressure sensors in mobile stations can be used to determine a mobile station's altitude above sea level (or other reference altitude) by comparing the measured barometric pressure at the mobile station's location (coordinates (x,y)) with the barometric pressure theoretically at the reference altitude at the same horizontal coordinates (x,y). The computed pressure difference can then be used to calculate the mobile station's altitude above sea level. Without knowledge of the theoretical atmospheric pressure at sea level (or some other reference altitude), the mobile station's altitude cannot be determined.
The barometric pressure at sea level is typically available through a network of weather stations. Weather stations, however, are usually only coarsely deployed in specific geographic locations (e.g., airports, etc.). To obtain the barometric pressure at sea level at locations other than the weather stations, the pressure data obtained from the network of weather stations needs to be interpolated (in space and time). Problems arise when timeliness and the geographical density of weather stations are not high enough to provide an accurate barometric pressure reference throughout the mobile station's service area at an arbitrary time. Under these circumstances, the calculated altitude may lack accuracy and—depending on the particular application—may not be usable at all (e.g., first responders trying to determine the floor number within a building of a caller in distress).
Therefore, what is needed is a manner to more accurately determine an altitude of a mobile station.